Previous gas scrubbers have utilized commonly known forces such as impaction, interception, diffusion and phoretic forces to assist in the removal of suspended contaminants or absorb gases from gas streams. These conventional scrubber columns have in general, operated at low gas velocities such that so-called "plug" flow was assumed to exist. For example, packed tower scrubbers operate at 4-5 feet/second; tray towers in the range of 6-8 ft/sec. and, spray tower scrubbers at approximately 8 ft/sec. In an effort to make these devices more compact and less expensive, gas velocities have been increased in recent years.
Tray scrubbers have suffered from distribution problems, thus requiring weirs, downcomers, baffles and other problem-causing internal devices. Packed towers require liquid distributors, gas injection grids, packing and other materials, all of which cause an unnecessary resistance to air flow, while reducing the overall efficiency and gas handling capacity of the scrubber system.
Fluidized bed type gas cleaning devices, in contrast, operate at higher gas velocities and use the motion of the gas stream as it passes through a dispersed liquid to generate a high liquid to gas surface area. Contaminant gases then diffuse to the liquid surface at which point they are absorbed and removed from the gas stream. Numerous studies have shown that increasing the surface area of the liquid and agitating the contact zone enhances the transfer of the gas into the liquid. We see this every day when we stir(agitate) things in order to better mix them.
The inventor herein secured protection for a revolutionary gas scrubber in U.S. Pat. No. 4,432,914. This is known in the engineering community as the catenary grid scrubber design.
This is an improved gas-liquid contact device which utilizes a specially contoured, free hanging catenary grid member(s) interposed in the gas flow within the device. It recognizes the fact that gas does not flow as a flat "plug" through a vessel. Instead, the gas flow forms a parabolically shaped pressure front which has velocities greater in the center of the vessel, diminishing to zero at the wall. The patent describes a catenary grid design which approximates the mirror image of the velocity pressure profile of the gas stream. When scrubbing liquid is injected free flow onto the upper surface of the grid and gases are directed in a counter flow direction at the design velocity, the liquid "fluidizes" (or ebulates) creating an area of great turbulence and mixing. The result was that the catenary grid scrubber achieved high efficiency in both particulate removal and gas absorption operating at gas velocities on the order of 18 ft/sec.
It has been observed however, that this catenary grid scrubber design has certain deficiencies. These shortcomings include, but are not limited to, the following:
1. the fluidized (ebulating) zone can become unstable, with openings forming through which contaminants can pass; PA1 2. the design makes it difficult to make in replaceable format (to retrofit existing towers); PA1 3. it typically has an open area of only 40-80% on any horizontal plane and therefore exhibits a higher than optimum pressure drop; PA1 4. it demonstrates limited gas volume turndown (typically 10-25% maximum); PA1 5. it runs at vertical velocities limited by the draining capacity of the grid; and, PA1 6. it does not induce significant horizontal components into the gas stream to aid in particle collection through increased impaction into the liquid. PA1 where .omega. is the angular velocity of the earth; .nu. is the speed of the body's motion; PA1 and .phi. is the earth's latitude.
It is widely known that the total energy input to a gas cleaning device largely determines its particulate removal performance. This is generally called the "equivalent energy theory". The greater the energy input, the greater the collection. The practice to date has involved the use of "man made" energy inputs provided either by moving the gas (velocity pressure) using a fan or similar device or by moving the liquid (pumping pressure) or combinations thereof. One way to maximize the efficiency of a gas scrubber, would be to use alternative low cost "natural" energy sources; or to use the latter as a supplemental means to augment the man-made sources. One of those natural "sources" is the apparent, or inertia force known as the Coriolis force or as the deflecting, or deviating, force due to the acceleration caused by the rotation of the Earth itself.
The Coriolis effect, or force, is named after the French engineer and physicist Gaspard Coriolis. This force affects an object moving in a rotating system (such as the earth), while being influenced by Newtonian forces when considered in a rectangular coordinate system. The Coriolis effect is sometimes called a "fictitious" force because it must be included mathematically in describing movement in a rotating system, though it is less evident physically.
Mathematically, the magnitude of the horizontal component of this inertia force per unit mass is given by the expression: EQU Coriolis Force=2.omega. sin .phi..nu.,
For a given speed, the Coriolis force is therefore at its maximum, 2 .omega.v, at the poles, and at its minimum, zero, at the equator. It acts at right angles to the radial motion of the object. Since it does not act in the direction of motion, it does not serve to speed up or slow down the object. It acts as an "inertia" force, establishing a resistance to any subsequent change in the object's motion.
Though the Coriolis Effect is a naturally occurring effect at all areas of the earth except the equatorial area, it is a subtle force. We can experience it personally when we walk on the surface of a rotating carousel. It is most noticeable in everyday life when water flows down a drain. A spinning vortex will form as the water drops down the drain. The relatively heavy water prefers to take a spinning motion rather than fold onto itself in part by the Coriolis Effect curving the net liquid flow of the stream furthest from the equator. The energy expended in spinning the liquid follows Newton's laws of motion in that the rotational force is related to the mass of the component in motion (i.e. the water) from F=ma, where m=the mass and a=the acceleration of that mass.
The invention uses the naturally occurring Coriolis effect to enhance the spin of water in a scrubber and thereby increase its particulate removal capability and impart greater stability to the fluidized zone at the higher operating gas velocities with minimum input of "man made" energy. The gas flow's energy is first used to create a "fluidized" or ebulating zone of liquid and thereafter the liquid-gas zone is caused to spin by harnessing the "natural" Coriolis force. The vertical component of the moving gas supports the ebulating zone and a special spin inducer helps control the spin of the zone by providing slight resistance to flow in an outward direction (much like the basin of a sink helps to control the vortex created by draining water). The stability is enhanced due to the polar moment of inertia which results from the rotating fluidized zone about a pivot axis. This is the same as the stability exhibited by a rotating top.
The Coriolis scrubber is designed to permit the swirling action to occur in a controlled ebulating zone through which gas or gases may pass. The spinning motion is intended to create a vector component of the velocity of the particle and that of the liquid such that the particle must move sideways in order to avoid capture. The particle however, given its inertia, tries to move straight ahead. This swirling action imparts a force on the particle which otherwise would not be available. The swirling action, most importantly, is created without excess mechanical input. The force of gravity and the rotation of the earth impart the motion.
The ebulating bed in the Coriolis effect scrubber (CES) is significantly different than the fluidized bed created in the catenary grid scrubber. In the latter, the gases are caused to flow through a curved wire mesh grid. This grid helps compensate for the velocity pressure profile of the moving gases. The gas velocity is essentially all vertically upward. The zone above the grid is basically a random, turbulent zone wherein the gases move axially up the tower. In the CES, however, no such wall to wall velocity pressure profile exists. Instead, the gases and/or the scrubbing liquid are caused to spin through the introduction methods of the liquid and/or gas and a central drainage area that helps induce the Coriolis driven swirl. Since a fluidized or ebulating bed is produced with a density far less than that of water (about 1/10th of that of water), and the Coriolis effect is reduced, it is still significant.
The present invention reduces or eliminates the non-uniform (random) mixing problem that can sometimes occur with the caternary grid and provides needed stability to the fluidized zone. It also provides greater solids separation given both the swirl induced centrifugal force plus impaction.
It also has superior droplet control since the liquid droplets are thrown towards the wall with few passing directly up the tower. In mass transfer devices, this effect is seen in devices which spin liquid/droplet streams in order to separate them. If the stream is given a tangential velocity, let's say in a vertical cylindrical vessel, it becomes a rotating system. Liquid droplets are affected by the Coriolis acceleration tending to be more easily separated if the cyclonic separator has a counterclockwise rotation north of the equator. The whirlpool occurring at the conical base of the separator will also separate better if allowed to spin in this same direction.
It is therefore a primary object of this invention to provide a mechanism for harnessing the "free" energy of the rotation of the earth to enhance particulate and contaminant gas control in higher gas velocity mass transfer devices.
It is also a principal object of the present invention to provide a gas and liquid contact apparatus which is a compact and energy efficient gas absorption and particulate removal device.
It is yet another object of this invention to provide a highly reliable apparatus for applications where the gas stream or liquid stream may contain components that could plug other designs in that the instant invention has an extremely open grid mesh design which resists plugging from gas borne or liquid borne solids.
It is still another object of this invention to provide an apparatus that is simple in design and operation with absolutely no moving parts.
Yet another object of this invention is to provide a device that has exceptional gas handling or throughput capability with over 4-6 times the gas handling capacity of most other scrubbers.